Compensation in terahertz time domain spectroscopy having two delays

Abstract

An information acquiring apparatus includes a light source portion for generating pulse-shaped pump light, and first and second probe light in synchronization with each other. A generating portion generates terahertz pulses when irradiated with the pump light. A detecting portion detects pulses of terahertz radiation from the object. A first delay portion adjusts an optical path difference between optical paths of the pump light and the first probe light reaching the detecting portion, so that the detecting portion detects a field intensity of a fixed point on the time domain waveform of the terahertz pulse from the object, following the fixed point. A second delay portion adjusts an optical path difference between the optical path of the pump light and the second probe light reaching the detecting portion by a sum of an additional optical path adjustment amount and the optical path difference, so that the detecting portion obtains the time domain waveform. A correction processing portion compensates for influence of a change in condition of the object on the time domain waveform, using the field intensity of the fixed point, or the adjustment amount adjusted by the first delay portion.

What is claimed is: 
     
       1. An information acquiring method for acquiring information of an object by using terahertz time domain spectroscopy, the method comprising:
 a first generating step of generating pulse-shaped pump light, first probe light and second probe light in synchronization with each other; 
 a second generating step of generating pulses of terahertz radiation by using the pump light; 
 a detecting step of detecting pulses of terahertz radiation from an object irradiated with the pulses of terahertz radiation; 
 a first delay step of adjusting an optical path difference between an optical path of the pump light used in the second generating step and an optical path of the first probe light used in the detecting step, so that a field intensity of a predetermined fixed point on a time domain waveform of the pulse of terahertz radiation from the object is detected in the detecting step, following the predetermined fixed point; 
 a second delay step of adjusting an optical path difference between the optical path of the pump light used in the second generating step and an optical path of the second probe light used in the detecting step by a sum of an additional optical path adjustment amount and the optical path difference adjusted in the first delay step, so that the time domain waveform of the pulse of terahertz radiation from the object is obtained in the detecting step; and 
 a correction processing step of compensating for influence of a change in condition of the object on the time domain waveform obtained in the detecting step by using the field intensity of the predetermined fixed point, or an adjustment amount of the optical path adjusted in the first delay step. 
 
     
     
       2. An information acquiring method according to  claim 1 , wherein the change in condition of the object is a change in thickness of the object, or a change in density of the object. 
     
     
       3. An information acquiring method according to  claim 1 , wherein a component or particle size of the object is recognized based on the time domain waveform of the pulse of terahertz radiation from the object corrected in the correction processing step.